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2025
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Determination of Chloride Content in Soil by Fully Automated Potentiometric Titration
I. Introduction
Chlorine is an essential nutrient element for all plants. It is widely present in soil and plants, with varying concentrations depending on the plant and soil type. Chlorine has multiple physiological functions and effects. Plants are highly sensitive to chloride ions; both deficiency and excess can be harmful. Therefore, determining soil chloride content is crucial for fertilization.
This method uses the JH-T6 fully automated potentiometric titration method from Shanghai Jiahang to determine chloride ion (Cl-) content. Based on the principle of precipitation, silver nitrate (AgNO3) standard solution is used to titrate chloride ions (Cl-). A white precipitate of silver chloride forms before the equivalence point. The amount of silver nitrate standard solution consumed determines the chloride ion (Cl-) content in the soil. The pH of the solution should be between 6.5 and 10.5 during the test.
II. Instruments and Reagents
2.1 Instruments
JH-T6 fully automatic titrator, silver ion selective electrode, analytical balance, etc.
2.2 Reagents
Silver nitrate standard solution (0.04 mol/L), 0.02 mol/L sodium bicarbonate solution.
III. Experimental Methods
3.1 Analytical Procedure
3.1.1 Soil Sample Preparation
Accurately weigh 50.0 g of air-dried soil sample (passed through a 2 mm sieve) using a balance and place it in a dry 500 mL Erlenmeyer flask. Accurately add 250 mL of carbon dioxide-free pure water using a graduated cylinder, stopper the flask, and shake for 3 min.
Depending on the ease of filtration of the soil suspension, use one of the following methods to obtain a clear leachate. Collect the filtrate in a dry Erlenmeyer flask. After complete filtration, thoroughly mix the filtrate, stopper the flask, and prepare it for analysis.
Soil suspensions that are easy to filter: Filter using filter paper through a 7 cm diameter funnel, or use a Buchner funnel for suction filtration. Cover the funnel with a watch glass to reduce evaporation. The initial filtrate is often cloudy and must be filtered repeatedly until clear.
Soil suspensions that are more difficult to filter: Filter repeatedly using a tightly folded double layer of filter paper through a 10 cm diameter funnel. Suspensions from alkalized soils and heavy clay soils with very low total salt content can be filtered using a plain porcelain filter candle. If suction filtration is not used, centrifugation can be employed; the separated solution must also be clear and transparent.
3.1.2 Determination of Chloride Content in Samples
Add 0.02 mol/L sodium bicarbonate (approximately 3 drops) dropwise to the soil leachate for titrating percarbonate and bicarbonate until the solution just turns yellow (pH 7). Then, use a potentiometric titrator to add 0.04 mol/L silver nitrate until the titration reaches the endpoint of the potential jump. Record the volume (V) of silver nitrate used. If the chloride content in the soil leachate is very high, reduce the amount of leachate used and take a separate sample for testing.
Set the titrator parameters as shown in Table 1:
Table 1 Titration Parameter Settings
3. Test Spectrum Example
IV. Results and Discussion
4.1 Experimental results are shown in Table 2:
Table 2 Test Results
4.2 Conclusion
Since the chloride content in the sample was low, it is recommended to use the equal volume titration (second derivative) method to determine the chloride content. The test results showed good repeatability and met the detection requirements.
References
[1] LY/T 1251-1999 Analysis of water-soluble salts in forest soils [S]
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